Chapter 1. Between the Wars

The Lessons of World War I

There does not seem to have been any high level discussion paper on the lessons of the submarine war of 1914–18. In part, this may have been a result of excessive secrecy, particularly with regard to intelligence, direction-finding, etc.¹ The notes that follow are based on hindsight.

The first lesson was that the UK was very close to defeat in 1917 and remained vulnerable to submarine attack. The German U-boat force had three main objectives: to weaken the Grand Fleet by attrition, so that the High Seas Fleet could fight on level terms; to defeat the UK by starvation; and to prevent the US Army from reaching France.²

The U-boats failed in all three. Attempts to attack the Grand Fleet and US army transports had negligible results. At the end of 1916 a German report estimated that sinking 600,000 tons of merchant shipping per month would bring victory within five months. The losses in 1917 were terrible but monthly sinkings only twice exceeded 600,000 tons. Attacks on merchant shipping came close to success but were defeated mainly by the introduction of convoy. Even so, large numbers of escorts were needed. ‘Hunting’ without precise location was of no value.

The enormous building programme of merchant ships (and escorts) in the USA was a major contributory factor. This was only partially offset by the building of U-boats, which by 1918 had steadied at about eight boats per month. There were concerted efforts to increase the building rate, but with little success. It is probable that the bottleneck lay in the supply of auxiliaries such as pumps, periscopes, etc., whilst training of crews – commanding officers in particular – remained a problem. However, defence analysts in the late thirties would have been wise to expect Germany to achieve at least an equal rate of completion of submarines.

Cachalot, a World War I escort based on a whale catcher. She was used in numerous trials of early asdic development.

Tactically, the increasing number of night, surface attacks in 1918 should have been noted, though these were solo attacks and not the wolf pack attacks of the later war. It should also have been recognised that even in 1917 U-boats could reach the east coast of the USA from German bases. The lengthy building time for U-cruisers, together with their relative lack of success, was misread and most big navies began to build ‘monster’ submarines.³

After the war there seems to have been a comfortable feeling that submarines had been defeated without the use of asdic, while whispers of this new sensor suggested that submarines had lost their cloak of invisibility. There were attempts to agree an international ban on submarines but they were never likely to succeed. Indeed, the RN submarine-building programme for the Far East suggests that it was recognised that a ban was never likely to be agreed. There was agreement that any submarine attacking a merchant ship would obey Prize Rules on safety of the crew, etc. but it is likely that there was little confidence that this would be maintained.

The Threat

In the 1920s there was little or no submarine threat to British merchant shipping. The USA had been ruled out as a potential enemy in the early years of the century and though the build up of French bombers and submarines was a matter of concern, the Entente Cordiale still held. Japan was seen as a potential enemy and was building a considerable number of fleet submarines but it was believed (correctly) that Japanese doctrine saw these boats as of use against an enemy battle fleet rather than merchant shipping.

Under the Versailles Treaty, Germany was forbidden to build or own submarines. However, as early as 1922, a design bureau, N V Ingenieurskantoor voor Scheepsbouw (IvS), was set up at The Hague to preserve German expertise by designing submarines for other nations. In 1926 they received an order for two boats from Turkey and trials were carried out in 1928 with German personnel. Also in 1928 an order for three boats was received from Finland. These went on trials in 1930, again with German crews. In 1934 another Finnish boat, Vessiko, the prototype of the later Type IIA of the German Navy, went on trials with a mixed Finnish and German crew. Later she was used to train German submarine crews. The Admiralty was aware of these developments⁴ but saw them as not a serious threat and even, perhaps, a bulwark against the Soviet Union.

On coming to power, Hitler’s Nazi Party renounced the treaty restrictions of Versailles and began to produce material for a submarine fleet. Construction of the Type IA began in 1935; this type was based on a boat ordered by Spain as E1 but sold to Turkey before completion. The Type IA seems to have been unsuccessful, as only two were built. They were followed by the 250-ton Type IIA, which completed only four months after they were laid down, as so much preparatory work had been done. Their main function was crew training but the British Admiralty saw them as designed for Baltic operations against the Soviet Union.

The Anglo-German Treaty of December 1935 limited the tonnage of the German submarine fleet to 45 per cent of that of the RN but with an escalator clause permitting an increase to equality in the event of a threat from a third party, after discussion. This clause was invoked in December 1938 without discussion.

Budgets

During the 1920s and early 30s, expenditure on the Navy was very tight. Battleship-building was forbidden under the Washington Treaty, extended by the London Treaty to 1937, but available building funds went mainly on cruisers and destroyers. A very few sloops were built as prototype minesweepers and escorts that could be used in peacetime as colonial policemen. It should be remembered that the Army and the RAF were, if anything, even worse funded than the Navy.⁵

The development of asdic, discussed later, gave priority to research and prototype units rather than an early production fit. Improvements followed each other rapidly and with no serious threat this may be seen as a wise policy. It did result in the A class destroyers and a few sloops completing ‘for, but not with, asdic’, although this was remedied before the war. Some effort was put into the development of an ahead-throwing weapon (see photo of Torrid) but this was abandoned because asdic technology was not then accurate enough to direct such a weapon without major work. Resources were scarce and needed for work seen as higher priority.

Torrid was used for trials of an ahead-throwing A/S weapon in the early 1930s. Mounted in A-position, it fired a stick bomb up to 800 yards. Target location with the asdics of the day was not good enough and effort was not available to cure the problems.

Tactics and Training

The flotilla at Portland developed the tactical use of asdic and in so doing exposed most of its weaknesses. In particular, the bending of the asdic beam by layers of water of different density was known, mainly from trials in the Mediterranean, though the full effect was probably not appreciated until the Spanish Civil War and the Neutrality patrols.

Exercises with submerged submarines were not, with rare exceptions, permitted after dark, though a few night exercises took place using surfaced submarines – surely more dangerous? Hence the value of night surface attack by submarines was known to some extent.⁶ There was a lack of awareness of the extent to which night surface attack was employed in the last year of World War I. Detection of a low-lying submarine by eye on a dark night is very difficult, a problem only solved when effective radar sets became available. Overall, those involved in ASW had developed effective weapon systems controlled by asdic, and tactics to employ these systems. However, as Franklin has shown, ASW officers did not figure in the higher ranks of the Admiralty, who were not fully aware of either the capability of ASW forces or their limitations.

Early 1930s

A major review of ASW was carried out in 1932,⁷ when there was still no direct submarine threat to the UK. The potential threat was already seen as Germany, even though she had no submarines at that date and it was envisaged that the lengthy voyage round the north of Scotland would mean few U-boats on station. These few could be countered by the older destroyers of the A–I classes and earlier destroyers, and by the few sloops. It was recognised that minesweeping and ASW had differing requirements, particularly as to draught, and the convoy sloop departed from the minesweeper design. It is, perhaps, ironic that the Halcyon class minesweeping sloops spent much of the war as ASW ships. The east coast was seen as the danger area and a number of countermeasures were put in hand. That area of operations lies outside the scope of this book but we shall look at it briefly for the sake of completeness.

Picotee. She is typical of the early Flower class, which were the only escorts which could be built in numbers in 1939. She mounts a four-barrelled machine gun in place of her pom-pom. (WSS)

The aircraft threat was recognised as serious on the east coast and led to the Hunt class with a very heavy AA armament; a number of older V&W class destroyers were also modernised with a heavy AA armament. A new design of coastal sloop was designed to provide A/S protection. They were beautiful little ships but far too expensive to be built in numbers. Their draught was too small for optimum asdic performance, a fault made worse in the first six, where the weight calculations were in error and they floated nearly a foot lighter than the inadequate design figure.⁸

Much of the coastal escort force would be made up of trawlers, and a prototype conversion of a commercial-style trawler was fitted out. The ship chosen was the James Ludford, built for the Royal Navy in World War I but typical of older commercial trawlers. Her conversion was judged successful and formed the model for many more during the war. In addition, Basset, a prototype of a new-design ship on trawler style, was built. She, too, was successful and some 200 generally similar ships of the Isle and Dance classes were built during the war. It was recognised even before the war that trawlers were on the small side for A/S ships and a larger vessel was developed from a whale catcher. These ships entered service as the Flower class corvettes, discussed in the next chapter.

Convoy Organisation⁹

During the 1930s it was Admiralty policy that convoy would be introduced only when the enemy resorted to unrestricted warfare and losses of merchant ships became unsupportable. This doctrine was carried to extreme in earlier years, exemplified by a speech in a debate in Parliament in 1935 by Lord Stanley (Parliamentary Secretary) in which he trotted out all the old objections that had been shown to be insignificant in World War I – waste of time in assembly, reduction to the pace of the slowest, port congestion, etc.

However, in January 1937 a Shipping Defence Advisory Committee (SDAC) was set up, at the suggestion of Adm James.¹⁰ The committee was to bring together the numerous bodies involved from ministries, the navy, ship owners and technical experts. There were seven subcommittees on specific topics, such as strengthening decks for defensive armament (and arranging payment), communication between bridge and engine room, assembly ports, convoy organisation (including commodores), provision of secret code books, war risk insurance and handbooks.

The subcommittees reported to the main body in July 1937, when Adm James made clear the Admiralty policy ‘that the convoy system is considered by the Admiralty to be the most effective form of protection against surface, submarine or air attack’. In the July meeting, James assured them that convoy would be introduced as soon as there was a significant threat, and that there were sufficient escort vessels.

The vice-chairman was Paymaster Rear Adm Sir Eldon Manisty, who, as a commander, had been involved in convoy organisation during World War I. He was a tower of strength and undertook a worldwide tour in 1938 to visit and inspect assembly ports and their local organisation. He outlined to each commander-in-chief and the local naval control officer the organisation that would be needed and helped to find the staff required. From 1935 Adm Manisty had developed a new Trade Division within the Admiralty, together with a Naval Control Service to direct shipping. Many of these posts were filled by retired naval officers.

The organisation was tested in the 1938 Munich crisis and a very few loose ends tied up before the war. The sinking of the Athenia on 3 September was taken, probably incorrectly, as the start of unrestricted warfare and the convoy organisation set in motion. It worked well and there were few omissions.

Asdic Development between the Wars¹¹

During 1916 a small team of scientists at the Admiralty Experimental Station (AES), Parkeston Quay began to study the use of echo ranging with high-frequency sound.¹² The principle was simple: a transducer would send out a short pulse of high-frequency sound which would be reflected from a submarine or any other object in its path. The reflected sound would be picked up by the same transducer and the time from sending to reception would give the distance to the target, if the speed of sound in water were known, while the bearing was given by the direction in which the transducer was pointing. Though the principle was simple, implementation was far from easy; every phrase in the preceding sentences conceals difficult, practical problems.

Other early asdic trials were carried out with P boats similar to P40. (WSS)

By 1918 it had been found that quartz was the most suitable material for the transducers and these were cut by a firm of tombstone makers, with the help of the Geological Survey Museum. It was all very secret, though there were some useful exchanges with the French, who were working on similar lines.¹³

It was soon found that the transducers worked best if enclosed in a dome, which prevented noise from the water flow over the face from interfering with the signal. Initial trials in the summer of 1918 were carried out first in a barge on the River Stour and then under the drifter Hiedra. In October 1918 a prototype set was tried in the trawler Ebro II, which got good echoes at 600 yards. As a result a first batch of twenty production sets was ordered and fitting drawings prepared for several classes of escorts. The patrol vessel P59 and the whaler Cachalot were fitted. By early 1919, echo ranges of 1,100 yards were obtained under ideal conditions and a set fitted in P55 was developed into the first production set, Type 112, which had a fifteen-inch transducer housed in a retractable, cylindrical, canvas dome, permitting operation up to twenty knots. Detection ranges of 2,500–3,000 yards were obtained. Ship-fitting of the 112 set began in 1920 with the 1st A/S Flotilla at Portland – mainly P and PC boats with a couple of whalers.

Once the war was over, the pace slowed down and further delay was caused by a sensible rationalisation of research establishments. In post-war years the initial emphasis was on basic research. This was a wise decision as basic knowledge of the sea, of transducers and supporting technology was minimal, whilst each new design of set was an improvement on earlier ones. Setting this continual development against the lack of any real threat and the small navy votes, it was obvious that a large production plan would be unwise.

One of the first tasks in 1920–2 was an accurate determination of the speed of sound in water (about 1,510m/s, depending on density and salinity). There was an important trial in 1922, when the Rocket and the submarine H32 went into the Red Sea, Mediterranean, Marmara and the Black Sea to explore the effect of sea water temperature; the cement fixing the quartz to the backing plate failed. This trial also showed that the asdic beam could be bent by sea water layers of different density, a problem further explored in 1930 by P59 and H32 with a new Type 119 set.

Bending of the beam by density layers was only one of the problems of early sets. The beam could be reflected by objects other than submarines – ‘non-subs’ as they were known – such as shoals of fish, wrecks, rocks and even tide rips. Much depended on the ‘ear’ of the operator, though the introduction of the range recorder enabled him to see whether the object was moving. These sets gave range and bearing but only a slight indication of depth, determined from the range at which the target entered and left the conical sound beam. The significance of the lack of depth indication was not fully appreciated, as many of the trials and exercises were conducted near Portland where the sea was fairly shallow.

Sea trials in the 1920s showed that asdic sets could be used in passive mode to listen for the enemy. A submarine could detect a destroyer steaming at fifteen knots at 1,000 yards. Work on surface passive sets was stopped to make more effort available for active sets, though some effort was put into submarine sets and into making British submarines quieter in the light of known German interest in listening equipment. Similar trials showed that noise picked up by the asdic included noise from flow over the dome and cavitation on the propellers.

The original transducer (Type 112) consisted of a single layer of quartz sandwiched between two steel plates. By 1928 the transducer was a two-ply sandwich, and in 1935 a four-ply was introduced, which remained standard until after the war. Most were cut by a small firm of masons at Portland.

By 1939 all the inter-war destroyers of the A-I classes had been fitted with asdic. Foxhound in 1942 had changed little. A 3in AA gun has replaced one set of torpedo tubes and Y gun has been removed. She has an early radar at the remaining masthead.

Dome design presented problems. Until 1928 DNC would not allow the keel to be cut. Even when this was relaxed DNC would only agree to cut-outs of less than two frame spaces, say fifty-five inches. This was not conservatism, but recognition that existing structural design methods could not cope with breaks in the main structural member in the highly loaded slamming area. The height of the dome was limited to fifty-four inches by the height of the dock blocks. Many trials evaluated different domes and their position, some even with a human observer inside the dome. Materials were another problem; early domes of Duralumin lasted a few months only, before corroding away. By about 1930 a satisfactory fifty-four-inch dome was designed for the first ‘production’ fit in the B class destroyers, which raised operating speeds to twenty-five knots.

The earliest sets required the time for the sound pulse to travel to the target and back to be measured with a stopwatch and, indeed, a stopwatch was retained as a back-up throughout the war. The introduction of a recorder that would not only give the range but make a permanent record of where the echo had moved was a major advance. The development was headed by the echo sounder team, where funding was slightly less difficult. Lack of an accurate recorder was given as the main reason for abandoning the ahead-throwing weapon in the early 1930s. By about 1932 a recorder using sensitised paper and a very accurate drive motor had been produced; for the first time asdic had a memory, from which target speed could be deduced. This marked the coming of age of A/S weapon ‘systems’, as opposed to a collection of independent widgets, and the situation was further improved by an increasing number of training aids.

By the end of the 1920s it seems to have been agreed that all new destroyers should be designed for asdic but only alternate flotillas would be fitted. In 1924 the 6th Destroyer Flotilla of V&Ws (and the leader, Campbell) was fitted with Type 112. The design of a production set was not ready for the A class, so the B class was the first flotilla to be equipped (Type 119). The curtailed C class of four ships were not fitted during build but were equipped soon after. Later flotillas all seem to have been fitted on build. Type 119 became the standard pre-war destroyer set and was frequently updated. After Hunter was mined in 1937, a short-pulse mine detection attachment was developed. The D class had Type 121, with similar electronics to 119 but a gyro-stabilised transducer. It could operate to twenty-four knots and was also fitted in sloops from Bittern onwards. A further-development 124 appeared in 1924, which incorporated the range recorder and an improved amplifier. By 1937 it was being installed in those older destroyers that did not already have asdic.

By the early 1930s it was already clear that the numbers of A/S vessels would always be inadequate and consideration was give to the use of fishing trawlers. Two sets were developed: Type 122 for ships with a turbo alternator, and Type 123 for those with an HF motor alternator. Both had portable domes. For these slow ships, retractable domes were not needed.

By the spring of 1939 the Admiralty had brought the Operational Intelligence Room, the Surface Ship Plot and the Submarine Tracking Room to full readiness. By the outbreak of war, there were some 200 ships fitted with asdic, including 100 of the more modern destroyers, 45 sloops and older destroyers and 20 A/S trawlers. In addition there were a further 200 sets stockpiled for requisitioned trawlers.¹⁴ Quartz had to be imported and a stock pile was built up, with purchases of one to three hundredweight each year from 1935.

Admiralty R and S Classes¹⁵

These two classes saw the introduction of geared turbines to the standard World War I destroyer, entering service from 1917 onwards. Comparative trials between Romola and the ungeared Norman showed fuel savings of 15 per cent at eighteen knots and 28 per cent at twenty-five knots, which, combined with an increase in fuel stowage, gave a useful increase in endurance, quoted as 3,440 miles at fifteen knots in the R class and very slightly more in the S class. As built, they had a trial speed of about thirty-six knots and carried three 4in guns and four 21in torpedo tubes. By 1939 there were one surviving R class (Skate) and eleven S class.

Skate was the only survivor of the World War I R class destroyer. This model by Julian Glossop shows her late in the second war, with a radar tower aft and ten-pattern depth charge fit.

Displacement (tons): 905 (Skate 900), 1,220 full load

Dimensions (feet): 265 pp, 276 oa x 26¾ x 8½/10¾

Shp and speed (kts): 27,000 = 36 (32½ full load)

Fuel (tons), endurance (miles) @ (kts): 3,440 @ 15

Complement: 90

Table 1.1 shows the technical details of the R and S classes. Note that in this and other tables the figure for endurance is nominal. Though it is based on actual trials figures, the real endurance in war was much less. All boilers were kept on line most of the time and high speed was used quite often; consumption by auxiliary plant was much higher. While the endurance figures quoted should not be regarded as accurately reflecting performance in operation, they were measured in the same way for all classes and provide a basis for drawing comparisons between them.

The S class was the ultimate development of the standard destroyer of World War I. The two forward boiler uptakes were trunked into a single funnel, which enabled the bridge to be moved aft and thus reduced the perceived motions. The sheer was increased and the stem slightly raked. For their day they were seen as good sea boats though soon overshadowed by the V&Ws. During the thirties several were modified for special tasks and as minelayers, while other changes were made for Operation Catherine.¹⁶ Perhaps surprisingly, those in Western Approaches soon reached a fairly uniform style.

Above and below: Two views of Scimitar: the one with white pendant numbers dates from 1940 and shows the beauty of these fast but fragile ships. The other picture is about a year later and the machine guns have been replaced by 20mm Oerlikons. The quarterdeck is congested with fourteen-pattern depth charge fittings.

These units had a single 4in in A-position and a 12pdr HA amidships. Initially, they had the heavy fourteen-pattern depth charge outfit (eight throwers and two rails) but this was reduced to ten-pattern in most, with only four throwers. They had Type 133 asdic and 286 radar, replaced in most by 291, though Skate and Shikari had 271 on a short lattice mast aft. Their elderly engines could still drive them at over thirty knots on a calm day, and these beautiful ships made a fine sight at speed.¹⁷ They had more power for their size than any other Western Approaches ship and were a delight to handle.

However, they had never been intended to be driven hard in rough weather and damage was frequent. Some lost a funnel; boats were so frequently lost that they were no longer issued with motor boats. The bridge front was often damaged; one captain was killed in his bunk in the sea cabin. Reluctantly they were soon paid off or used for training. The Admiralty is often criticised for scrapping ships between the wars that would have been valuable in the war to come – ninety-seven ships of the R and S classes were scrapped. But did we really want to spare crews and maintenance facilities for ships like these?

Older Destroyers (V&W, Leaders)¹⁸

The V&W classes, with their leaders, were the finest destroyers of World War I. Others may have been more heavily armed or faster but the V&Ws seem to have achieved the best balance of military qualities. Their design by C D Hannaford shows how rearrangement of conventional features can lead to a step change in capability. The introduction of the R class with a sea speed of thirty-four knots showed the need for a faster leader. A number of sketch designs were considered but the solution was to copy the superimposed guns forward from the Seymour class and use a similar arrangement aft. The new 4in Mk V quick-firer (QF) was fitted and, even allowing for the longer barrel, the ship could be a little shorter at 312 feet overall. A fifth 4in was considered but replaced by a 3in HA gun. The geared-turbine plant of the R class was adopted but the two forward funnels were combined so that the bridge could be a little further aft to make it dryer. Moving the bridge and the forward guns aft reduced the vertical accelerations perceived at those positions, adding to their reputation as good sea boats. Five V leaders were ordered, completing in mid-1917.

Veteran has full ASW equipment but did not receive a long-range conversion. She retains the forward torpedo tubes. (IWM A 7562)

Following Jutland there was a demand for more heavily armed destroyers and, after various possibilities were considered, it was decided to order twenty-one very slightly modified V class in July 1917. Four more followed the next month. Even more speed was wanted but speed is expensive and nineteen ‘repeats’ were ordered in December 1916, together with two modified ships from Thornycroft. However, proponents of gunpower won out and the sixteen ships (plus two Thornycroft specials) of the modified W class ordered in January 1918 were a knot slower but carried four 4.7in guns (nine were cancelled when the war ended). This gun was a breech-loader with a slower rate of fire but a 50lb shell instead of the 35lb of the 4in. The last nine ships had the long boiler room adjacent to the engine room, seriously reducing their ability to survive underwater damage amidships. The consequent rearrangement meant that the fore funnel was the thicker one and, more important, A and B guns moved a little further aft. In April 1918, thirty-eight of these modified ships were ordered (twenty-nine cancelled).

Displacement (tons): 1,090, 1,480 full load

Dimensions (feet): 300 pp, 312 oa x 29½ x 8½/11¾

Shp and speed (kts): 27,000 = 34 (32 full load)

Fuel (tons), endurance (miles) @ (kts): 367, 3,500 @ 15

Complement: 134

The Thornycroft specials were bigger (1,120/1,512 tons), faster (thirty-five knots) and more expensive than the Admiralty-design ships. This was mainly due to more powerful machinery but they ran trials on the St Catherine’s mile, where the effect of shallow water gave them a bonus of one and a half knots. This was not ‘cheating’; the benefit was well known both to Thornycroft and the Admiralty. They had the real advantage of greater freeboard.

Post-war destroyers did not enter service until the thirties, so for a decade the V&W class were indisputably the best. Even in the thirties the new destroyers of the A–I classes were of only slightly greater capability than the V&Ws, and the older classes were said to be more robust.

By 1939, twelve of these ships were gone – three sunk in World War I or its aftermath in the Baltic, one (Bruce) in trials of a torpedo with magnetic actuation, and the rest scrapped. Valhalla went in 1931, known to need an expensive refit. The four that were scrapped later had spent eleven to fifteen years in reserve, more damaging than the wear and tear of active service. Walrus ran aground whilst being towed to a WAIR refit.

Most of the rest had had a fairly eventful life between the wars. Though there was some wear and tear, this active life did ensure that they were well maintained. Most had been built with galvanised plating and framing.¹⁹ Galvanising seemed expensive and time-consuming during World War I but it paid off during the later war. Few changes had been made; twin torpedo tubes were replaced with triples (five exceptions) and asdic Type 121 (or later variants) was fitted. Very little had been done to improve living conditions, with mess decks poorly insulated and inadequately heated. The coal-fired galleys were obsolete. Hard-lying money was reintroduced during the winter months as partial compensation. The inter-war complement of 110–15 rose to 170 during the war

Malcolm, a leader, had much the same fit as Veteran.

A total of fifteen (plus Wallace) were converted to ‘WAIRS’ with a heavy AA armament of two twin 4in and two four-barrel machine guns. They were used almost exclusively on the east coast and played no part in the Battle of the Atlantic. Some thirty-eight of the remainder were available for Western Approaches work or preparing for such duties. Many had been in reserve until very recently and their crews had a high proportion of reservists, who took a little while to get back to efficiency. The Review of the Reserve Fleet at Weymouth just before the war helped to bring the crews up to standard.

Early changes were few; some vessels had a 12pdr HA in place of a set of torpedo tubes, Oerlikons were fitted when available and, later, radar was installed. AFOs in 1940 and 1941 approved the fitting of electric heaters and the installation of lagging and lining in mess decks but this work had low priority and was only carried out when the ship was in hand for a refit. As so often with lightly built, riveted ships, there were leaks in the forecastle deck into mess decks and through the shell into fuel and reserve feed tanks. Despite their age, the V&Ws seem to have been little worse than later destroyers. As Atlantic escorts, their main problem was lack of endurance, quoted at 2,180 miles at fourteen knots with some 370 tons of oil. Like all destroyers of both world wars, the low freeboard abaft the forecastle made fore and aft access very dangerous in bad weather. Only in the last Emergency classes were flying bridges installed above the torpedo tubes, making access merely uncomfortable.

Long Range Escorts

The V&Ws had three boilers, the majority of the ships having one boiler in the forward boiler room and two in the longer room adjacent to the engine room. Starting with Vimy in January 1941, the forward boiler was removed and the lower part of the boiler room converted into fuel tanks, increasing endurance to 2,780 miles at fourteen knots with 450 tons of fuel. The upper layer became an additional mess deck, sorely needed in these overcrowded ships. The complement had gone up to 160–70. The loss of a boiler reduced power to 18,000shp and speed to 24½ knots.

B and X guns (4in or 4.7in) were retained and A gun was replaced by Hedgehog. In some early conversions, Hedgehog was not available and A gun was retained briefly (Vimy, Vansittart).²⁰ Some retained one triple torpedo mounting for launching heavy Mk 10 depth charges. Initially they retained the 12pdr but this was generally removed to make way for more depth charges. Four or five Oerlikons were added. Radar types 271 and 291 were fitted and roughly half had HF/DF with asdic 144. Up to 150 depth charges were carried.

Vimy has had a long-range conversion but, unusually, retains A gun, presumably because her Hedgehog mount was not ready.

By August 1942 Whitehall had lost the experimental five-mortar fitting (See Chapter 7) and was a conventional Long Range Escort (LRE). She seems to have a ten-pattern depth charge fit.

Vidette is another standard LRE. (IWM HU 1445)

The big after funnel marks Viscount as a Thornycroft Special but otherwise is a standard LRE. (IWM A 10712)

In all, twenty ships were converted, eleven in the dockyards and nine in commercial yards, the work typically taking about six months, though there were considerable variations depending on the defect list and on other work in hand.²¹ An improved long-range escort (LRE) version was considered in January 1943.²² It had 4in guns in A and X positions, a Hedgehog behind A, a twin torpedo tube, and two twin and two single Oerlikons. There was a new bridge (not sketched) with a lattice mast. Another study was for a tanker version. All old machinery was removed and twin diesels gave a speed of fifteen to seventeen knots. She would have carried 711 tons of fuel and 200 depth charges for transfer. The guns and funnel were dummies.

Keppel (and her sister Broke) were the only two-funnelled LREs. Originally she had three boiler rooms and lost the forward one in conversion but still needed two funnels. (IWM A15039)

Keppel, a Thornycroft leader, was an interesting variant on the LRE theme. As built, she had four boilers in three boiler rooms (1:2:1), the uptakes trunked into two large, flat-sided funnels, and carried a total of 500 tons of oil (398 main, 102 peace tanks²³). On conversion, the forward boiler was removed and the lower part of the space converted to an 80-ton fuel tank, bringing her total capacity to 580 tons. This gave her an endurance of 5,700 tons at fifteen knots and a top speed (estimated) of twenty-five and a half knots, at which the endurance was 860 miles. A photo²⁴ shows her with a slender forward funnel. She is mounting two 4.7in, one 12pdr and three Oerlikons, together with Hedgehog, four depth charge throwers, two rails and two triple torpedo tubes. Later, in April 1944, she lost the tubes and probably the 12pdr and carried 140 depth charges. It is probable that Broke was similarly modified.

Major conversions of elderly tubs are rarely worthwhile but the Long Range Escorts seem to be an exception. They were still faster than most escorts and had the most modern A/S armament. The long-range conversion worked well because the original armament was on the upper deck and the removal of half the guns and the tubes helped to retain satisfactory stability.

Wallflower was a typical World War I sloop, a type intended for minesweeping but mainly used as escorts.

Early Sloops

During World War I a large number of Flower class sloops were built. Originally, their primary role was seen as minesweeping but increasingly they became used as escorts. An original requirement to carry up to 1,000 men, operating as a ferry, proved valuable since, without these men, there was a considerable stability margin. In post-war years a number of these ships were used as colonial policemen, but by the mid- to late 1920s they were wearing out.

Considerable thought was given to their replacements and it was originally intended to build two prototypes, one with steam turbine machinery and the other with diesel engines, but no suitable UK engines could be found.²⁵ Their wartime role was again primarily minesweeping, for which a shallow draught was seen as desirable (8 feet 6 inches was chosen). Later this shallow draught was seen as a handicap for asdic operation. Anti-submarine warfare was not neglected; it seems always to have been envisaged that they would have asdic. However, sets were not available and the early classes were completed without. By the outbreak of war they had been fitted with Type 127, replaced when Hedgehog was fitted by Type 144. Four depth charge chutes were held on board, disassembled; many chutes and rails were held in store after being removed when ships were disposed of after the first war. Two depth charge throwers were held in their home dockyard, as were the depth charges, many also dating back to the war.

Bridgewater was the first post-war design with many features of the earlier ships – including the big openings in the side which had to be closed to improve stability at large angles of heel. (John Roberts)

Wellington in 1935 with a quarterdeck full of minesweeping gear and not an A/S weapon in sight. Wellington is still (2007) afloat on the Thames as a club house but little more than the bare hull remains.

By 1943 Bridgewater had a full ASW fit with at least two radars and HF/DF.

The armament was intended to include two single 4in on HA (high-angle) mounts but, to save money, one was replaced by an LA (low-angle) mount from store. The LA gun was replaced in 1938 by an HA mount when the ships also received a quadruple 0.5in machine gun. It was intended that the second gun should be an alternative to the minesweeping winch, but they completed with both and the complement rose from seventy-six to ninety-six. Partly as a result of this weight growth, the stability of the first ships was poor, particularly at large angles of heel (vanishing angle 57º). They had been designed with a short, watertight forecastle though the deck itself continued well aft above openings in the side.²⁶ The large-angle stability was greatly improved by making the side watertight to the forecastle deck and by the addition of thirty tons of ballast. This simple stability problem suggests that their design was not taken seriously enough. The fact that there was no launching ceremony for the first four ships may be seen as a further example of their lowly status.

The 1927 Estimates brought orders for two ships, of the Bridgewater class (table 1.3). These two were followed by several very similar classes: four Hastings, four Shoreham, four Falmouth. The eight ships of the Grimsby class introduced changes in gun armament. Most had two 4.7in LA and one 3in HA. Aberdeen had a reduced armament of two 4in HA as a C-in-C’s yacht, while Fleetwood had two twin 4in HA (it seems likely that this was the intended armament of the whole class). The additional AA gun fit was of little value without fire control. According to Rowland Baker, the Grimsby was the first sloop with correct weight calculations.

Displacement (tons): 1,045, 1,360 deep

Dimensions (feet): 266¼ x 34 x 8¾/11½

Shp and speed (kts): 2,000 = 16.5

Fuel (tons), endurance (miles) @ (kts): 282, 4,500 @ 10

Complement: 95

Displacement (tons): 990, 1,300 deep

Dimensions (feet): 265 x 34 x 7¼

Shp and speed (kts): 2,000 = 16.5

Fuel (tons), endurance (miles) @ (kts): 300, 5,700 @ 10

Complement: 100

Mallard was designed as a small A/S escort for east coast work. They were too expensive to build in numbers.

Programme	Ships	Notes
1927	2 Bridgewater
1928	4 Hastings	+ RIN Hindustan
1929	4 Shoreham
1930	4 Falmouth
1931	2 Grimsby	+ Halcyon class minesweeping sloops
1932	2 Grimsby
1933	2 repeat Grimsby	+ RIN Indus and Kingfisher coastal sloops
1934	2 repeat Grimsby	+ 4 RAN

By 1931 it was obvious that the combined minesweeper/escort role was not appropriate and a new class of small minesweeping sloops, the Halcyons, was introduced. Ironically, most of them spent much of the war on A/S escort duties in the Arctic.

Wartime changes varied but the following is typical. They were fitted with a second quadruple machine gun in 1939. The machine guns were replaced by single Oerlikons in spring 1942 and two more (for a total of four) added in 1943 when Hedgehog was fitted²⁷ and asdic 144 installed. Radar 268 was fitted in 1941, replaced by 271 in 1942, and modified to 271Q in 1943, when some received 291 as well. HF/DF was fitted to most in 1942–3. The depth charge outfit was increased to forty at the outbreak of war.

The considerable number of fairly similar ships built over eight years shows that the naval staff were well satisfied. A consultation exercise in 1930 seemed to express satisfaction, though asking for heavier armament and an aircraft, both seen as impossible within the financial limits.²⁸ They were reasonable sea boats, with bilge keels sixteen inches deep (fairly high for the era) to reduce rolling, and sufficient length to limit pitch.

The Washington Treaty imposed no limits on smaller ships. The London Treaty (1930) placed no restriction on ships under 2,000 tons, a speed of less than twenty knots and an armament of no more than four 6.1in guns and no torpedoes. There were no limits on vessels of less than 600 tons.

Hawthorn was typical of many commercial trawlers converted for ASW. They were too small to carry a full range of ASW equipments and their operators.

Unst was typical of a very numerous group of Admiralty designs based on trawler practice.

The emphasis placed on escorts for coastal convoys in the early 1930s led to the design of the six coastal sloops of the Kingfisher class in 1934 (later reclassified as patrol vessels and later still as corvettes). They were designed to come under the 600-ton barrier of the London Treaty and looked like a toy destroyer. This emphasis on weight-saving was unfortunate as the design draught was on the low side for good asdic operation and they completed very light, with one foot less draught. At £160,000 and with turbine machinery they were far too expensive for mass production. Three modified ships of the Guillemot class were built under the 1937 Estimates. They had heavier scantlings to increase draught. None of these pretty little ships played any part in the Battle of the Atlantic, though they did good work on the east coast, which was what they had been designed for.

The older sloops participated in twelve U-boat sinkings. Note that turbine machinery made them unsuitable for mass production in war. Wellington is afloat on the Thames as a clubhouse but little of her original appearance or equipment survives. At the time of writing (2007) there is a serious proposal to bring Whimbrel back from Egypt and make her a Battle of the Atlantic memorial at Liverpool. She has not changed much from wartime appearance.

Trawlers

Trawlers played only a very minor part in the Battle of the Atlantic but it is worth giving brief consideration to the reasons for this. During the 1932 review of ASW, a shortage of coastal escorts was identified. The Admiralty took two positive steps to remedy this situation with prototypes of a converted commercial trawler and a new design built in the style of a commercial trawler, but with changes to make her more suitable as a coastal A/S escort.

The James Ludford had been built for the Admiralty during World War I as one of sixty-nine Mersey class but was entirely typical of a commercial trawler of her generation. She was given a 4in gun, asdic type 123 and twenty-five depth charges with two rails and two throwers. Sadly, she was sunk by a mine in December 1939.

Basset was the prototype for 211 vessels of the Dance, Isles, Tree and Shakespeare classes built during the war, including sixteen in Canada and eighteen in India. The structure was based on commercial trawler practice but the hull form was ‘warship’ style, based on model tests. Subdivision was much improved over commercial ships and accommodation somewhat better.

Displacement (tons): 438, 665 deep

Dimensions (feet): 138½ pp x 23¾ x 13½ mld

Speed (kts): 11

Fuel (tons), endurance (miles) @ (kts):

Complement: 20

Displacement (tons): 551, 775 deep

Dimensions (feet): 150 pp x 27½ x 13½ aft

Speed (kts): 13

Endurance (miles) @ (kts): 3,000 @ 9

Complement: 33

A Type VIIC U-boat at the war’s end. Deep diving and reliable, they were the backbone of Dönitz’s fleet.

During the war some 100 trawlers were converted into ocean escorts. Such ships were at least 160 feet long with a speed of eleven to twelve knots. Typically they would carry 200 tons of coal, enough for fourteen days’ steaming at economical speed, with three days’ reserve. They would have a 4in gun and one to three Oerlikons, with asdic in the 123 series, Type 268 PQ radar, four depth charge throwers, two rails and fifty-five charges. The armament fit was little inferior to a Flower and many escorts failed to match their endurance. They were seaworthy enough for fishing off Iceland. Why then did they feature so little in the Atlantic?

It was probably a combination of things. For example, in many requisitioned ships the deck over the hold was in bad condition and, where possible, it was replaced with a steel deck. However, in many ships stability was insufficient to permit this. No stability data were available for most ships and many were inclined. A minimum value of GM was set at twelve inches, with a freeboard of thirty inches in the larger vessels. Stability demanded ballast, whilst freeboard made this difficult. Extra equipment was mainly topweight and made stability worse. Lack of space for new, improved asdics and for radar, together with their crews, was probably the biggest factor. The crew of requisitioned trawlers was about half that of a Flower, which led to rapid exhaustion, particularly with the severe motions of a smaller ship. A few were used as rescue ships.

U-boats

A study of any of the standard reference books²⁹ will suggest that there were few technical developments in U-boat design between the wars. A typical comparison is shown in table 1.8. There are, however, two important omissions from this table: diving depth and sensor fit. In both cases they were seen as very important and hence were kept secret but, to some extent, their significance has not always been appreciated by modern writers.

In shallow waters, such as those round the British Isles, it is necessary only to know the position of a target submarine in plan – two dimensions. In deeper waters the problem becomes a much more complicated, three-dimensional one. A related problem is that it takes a long while for a depth charge to sink to the level of the submarine, making the fire control problem more difficult and increasing the opportunity for the boat to move out of lethal distance from the charge.

A different problem is the meaning of ‘diving depth’. One meaning is the depth at which the hull will collapse (see appendix I). This was calculated by an inexact formula and was subject to errors in building, while control errors mean that a submarine may not hold the intended depth.

For all these reasons a large factor of safety was applied in setting an operational maximum depth. Some idea of the depths involved may be seen in comparing figures for the Royal Navy’s S class. British practice of the day was to apply a factor of safety of about 2. Initially the Germans used a similar factor. Submarine COs were aware of this and would usually test dive to 10 per cent below the ‘safe’ depth. Designers were aware of this and even encouraged it on trials, having added 10 per cent to the safety margin. I have even noted reputable writers compare British safe depth with German collapse depth. In table 1.9, depths listed as ‘trial’ are those achieved in post-war trials when submarines were lowered until they collapsed.

A Type XI U-boat, bigger and longer-ranged than the Type VII.

German designers of the mid-1930s had the advantage of a more accurate method of calculating the strength of pressure hulls and framing. This enabled them to use lighter framing than British boats, putting the weight saved into thicker plating. They also had the benefit of weldable steel, thus saving more weight. The early Type VII U-boats were quoted as having a 100-metre safe depth and 200-metre collapse. It is likely that neither COs nor even designers were aware of the ultimate strength of these boats (see appendix I). COs soon found that the risk of exceeding 100 metres was much less than that of being within lethal range of a depth charge.

Post-war analysis suggests that the collapse depth of a Type VIIC was about 800 feet, though U-331 is said to have survived a dive to 876 feet. In the latter years of the war, 500 feet was used fairly frequently. The Type VIIC-41 had a thicker pressure hull, giving nominal diving depths of 120 metres and collapse at 250 metres, while the Type VIIC-42 was even thicker with depths of 200 metres and 400 metres. In both these latter classes the weight for the thicker pressure hull came mostly from lighter machinery. The Type IX and IXD had a diving depth of 100 metres and collapse at 200 metres, both often exceeded.

Particulars of the Type VIIC are given in table 1.8 (U-69). The bigger Type IX had a displacement (surface) of 1,144 tons and a length of 76.5 metres. They had four bow tubes and two stern. Surface speed was about eighteen knots. They were a development of the unsuccessful Type IA and very similar to the U-81 of 1915. It is said that Raeder was very enthusiastic for the bigger IXs, while Dönitz preferred the more manoeuvrable VIIs.

Nominal endurance is defined by fuel stowage: about 8,500 miles at ten knots for the VIIC from about 100 tons oil, 12,000 for the VIID from 160 tons of oil, and 13,850 at ten knots for Type IXC with 200 tons oil. This is an arbitrary figure and probably greater than would be achieved in war (see Type XIV U-boat, chapter 5). Effective endurance also depends on the number of torpedoes – eleven to twelve for VIIs, twenty-two for the IXs – and on supplies of food. U-boats would leave harbour with half their toilet cubicles full of tinned food and layers of tins on the floor of the passageway. Above all, endurance depended on that of the crew and there is no doubt of the dedication of U-boat men.

From about the date of the Anglo-German treaty the Germans decided to concentrate their acoustic work on passive (listening) sets. As a result, when war broke out, they had a mediocre active asdic set and a superb listening hydrophone. This was the Atlas-Werke GHG set used in wartime boats such as the Types VII and IX. Fittings varied slightly but in usual form there were forty-eight Rochelle salt hydrophones in two rows of horseshoe shape below the torpedo tubes. Typically, it could pick up a surface ship at ten miles, though a convoy could be heard at a greater distance. An escort coming in for a quiet attack at slow speed could usually be detected by the noise from her auxiliary machinery. The potential of this set was only recognised in August 1941 with the capture of U-570 (HMS Graph). In listening capability it was far superior to RN asdic in passive mode.

A Type VIIC, U-995, forms part of the U-boat war memorial near Kiel, while a Type IX, U-505, is shown at the Chicago Museum of Science. Type XIV (milch cows) and Type XXI are dealt with later. Both the Types IX and VII were excellent conventional submarines with pressure hulls stronger than those of other navies.